Multi-cycle downhole apparatus

ABSTRACT

A downhole apparatus which can be used as multi-cycle circulating subs utilized in downhole drilling operations, includes a piston ( 242 ) slidably mounted in a body between positions in which at least one aperture in the body is opened and closed. Movement of the piston ( 242 ) is controlled by a pin ( 86 ), secured to one of the body and a control member, and a control groove ( 52 ) formed in the other of the body and control member for receiving a portion of the pin. An arrangement of elements ( 232, 276 ) respectively connected to the control member and body is such as to normally resist axial movement of the control member from a first axial position to a second axial position. A spring ( 44 ) is located in a chamber for biasing the piston ( 242 ). The chamber is vented by an opening in the body.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to downhole apparatus and particularly,but not exclusively, to multi-cycle circulating subs used duringdownhole drilling operations.

2. The Prior Art

It is often necessary in downhole drilling operations to bypass orpartially bypass the flow of wellbore fluid down the drill string intothe wellbore annulus. For example, this may be necessary where thedesired fluid flow rate to drive a drilling tool is insufficient tocarry all the drilled material up the annulus to the surface. In thesecircumstances, a circulating sub may be used to allow the flow raterequired to remove the drilled material to be pumped into the annuluswhilst maintaining the lower flow rate required at the drilling tool.

It is known to provide a circulating sub with an axially movable pistonfor opening and closing vent apertures. The vent apertures are providedin a body of the sub and allow wellbore fluid pumped downhole through acentral bore of the sub to pass into the surrounding wellbore annulus.Opening and closing of the vent apertures by means of the piston iscontrolled by a pin and groove arrangement. The pin is located in one ofthe piston and body and is received within the groove provided in theother of the piston and body. The profile of the groove is such thataxial movement of the piston results in rotation of the piston withinthe body. Furthermore, the extent of axial piston movement is limited bythe groove profile. Thus, the piston may be moved axially downhole bymeans of a predetermined fluid flow rate and returned uphole by means ofa biasing spring so as to cycle the piston into a position wherein thecontrol groove permits subsequent movement of the piston from a ventaperture closed position to a vent aperture open position.

A problem associated with the aforementioned prior art means forcontrolling the piston is that there can be a tendency for the controlpin to become damaged within the control groove as a result of axial androtational forces acting on the piston. These forces can shear thecontrol pin within the control groove.

In addressing this problem, our UK patent application number 0116472.2provides apparatus comprising a piston slidably mounted in a bodybetween positions in which at least one aperture in the body is openedand closed. Movement of the piston is controlled by one or more pins(secured to one of the body and a control member) and a control groove(formed in the other of the body and control member) in which a portionof the or each pin is received. An arrangement of elements respectivelyconnected to the control member and body is such that, as the controlmember moves axially, lengths of said elements locate adjacent oneanother so as to provide resistance to relative rotation in at least onedirection of the control member and body. The relative rotation is arotation which presses the control member against the control groove.The elements are also arranged to limit axial movement of the controlmember. The apparatus thereby provides means by which the risk of damageto the control pin is reduced.

The present invention provides apparatus for selectively providing fluidcommunication between the interior of a downhole assembly and theexterior thereof said apparatus comprising: a body incorporating a wallprovided with at least one aperture extending therethrough; a pistonhaving a longitudinal bore extending therethrough and being slidablymounted in the body so as to be movable between a first positionrelative to the body preventing fluid communication between the bore ofthe piston and the exterior of the body via the or each aperture and asecond position relative to the body permitting fluid communicationbetween the bore of the piston and the exterior of the body via the oreach aperture; and controlling means for controlling the movement of thepiston between the first and second positions, the controlling meanscomprising: a control member slidable in the body and movable by fluidpressure in the body in a first axial direction relative to the body; aspring biasing the control member in an opposite axial direction of thebody; a pin secured to one of the bodes and the control member; and acontrol groove in which a portion of the pin is received formed in theother of the body and the control member, the control groove beingshaped to limit axial displacement of the control member generated bypressure variations in the body such that only after a predeterminednumber of movements of the control member to a first axial position isthe control member able to move to a second axial position so as todisplace the piston from one of the first and second piston positions tothe other of the first and second piston positions; wherein thecontrolling means further comprises a first element connected to thecontrol member so as to prevent relative rotation between the firstelement and the control member, and a second element connected to thebody so as to prevent relative rotation between the second element andthe body, wherein the arrangement of said element is such that, in thefirst axial position of the control member, the first and secondelements normally abut one another so as to resist axial movement of thecontrol member toward the second axial position, said elements locatingoffset relative to one another so as to allow movement of the controlmember to the second axial position only after a predetermined number ofmovements of the control member to the first axial position; and whereinthe spring is located in a chamber defined between the control memberand the body, and at least one vent opening is provided in the body forventing fluid located in the chamber to the exterior of the body. Thearrangement of said elements may be such that, as the control membermoves from said first axial position to said second axial position,increasing lengths of said elements locate adjacent one another so as toprovide resistance to relative rotation, in at least one direction, ofthe control member and body, said relative rotation being relativerotation which presses the control pin against the control groove.

Thus, in apparatus according to the present invention, movement of thecontrol member past the first axial position is normally prevented by anabutment of the first and second elements and, as a consequence, anundesirable application of axial pressure by the control groove on thecontrol pin may be avoided. Also, as the control member moves from thefirst axial position to the second axial position and thereby displacesthe piston into one of the first and second piston positions, elementsconnected to the control member and apparatus body locate adjacent oneanother so as to provide resistance to relative rotation of the controlmember and body. As a consequence, relative rotation which tends topress a control pin against the control groove can be resisted anddamage to the control pin thereby avoided. The first and second elementsmay be arranged so as to allow relative rotation between the controlmember and body as may be permitted by the control groove profile.However, the elements do not allow rotation which will press the controlpin and groove against each other to the extent that damage to the pinmay occur. Furthermore, as the control member is moved from said firstaxial position to said second axial position, the elements locateadjacent one another to an increasing extent by virtue of said elementssliding over one another in a collapsing telescoping type of movement.Thus, as the control member moves towards the second axial position, theelements are better able to resist relative rotation due to theincreasingly long lengths of element portions located adjacent oneanother. Also, since the spring chamber may be exposed to wellbore fluidpressure, a resultant fluid pressure may be applied to the controlmember which, in use, reduces the risk of an accidental cycling of thecontrol pin within the control groove.

Ideally, at least one vent opening is provided in the control member forventing fluid located in the chamber to the exterior of the body. The oreach vent opening in the control member or the body may also be occludedso as to prevent a passage of fluid therethrough. The or each occludedvent opening may be occluded with a removable plug. Thus, the springchamber can be vented to the piston bore or wellbore annulus dependingon which set of vent openings are occluded.

It is also desirable for the axial movement of the piston to be limitedby one or more stop shoulders provided on the body. A first shoulder maylimit axial movement of the piston in a first direction. A secondshoulder may limit axial movement of the piston in a second directionopposite to said first direction. In this way, the application of axialthrust forces to the or each pin with the piston in the uppermost andlowermost positions may be avoided.

It is preferable for said first element to remain axially spaced fromsaid second element until the control member is axially moved to thefirst axial position. The arrangement of the first and second elementsmay be such that said elements become offset to one another, so as topermit axial movement of said elements past one another, only after saidpredetermined number of movements of the control member to the firstaxial position. The said elements may be offset angularly. It is alsopreferable for the arrangement of the first and second elements to besuch that, when said elements are offset so as to permit their axialmovement past one another, the control pin is received in one of aplurality of portions of control groove allowing the control member tomove to the second axial position. The arrangement of the first andsecond elements may also be such that, when said elements are offset soas to permit their axial movement past one another, the control pin isreceived in a portion of control groove allowing the control membereither to displace the piston in said first axial direction from thefirst piston position to the second piston position and then to a thirdpiston position preventing fluid communication between the bore of thepiston and the exterior of the body via the or each aperture, or todisplace the piston in said first axial direction from the second pistonposition to the first piston position and then to a third pistonposition permitting fluid communication between the bore of the pistonand the exterior of the body via the or each aperture.

The control groove may comprise a plurality of said portions allowingdisplacement of the piston to said third piston position. Movement ofthe control member in said first axial direction past the second axialposition may be prevented by means of an abutment of the second elementwith the control member or a component connected thereto. The secondelement may also be releasably connected to the body. The second elementmay be releasably connected to the body by means of a shear pin. When inthe second piston position, the piston may be located so as to seal afluid pathway through the apparatus and thereby, in use, direct fluidflowing into said apparatus through the or each aperture. Also, the oreach aperture may be arranged so that wellbore fluid flowing in usethrough the or each aperture from the interior of the apparatus isdirected in a direction having a component parallel to the longitudinalaxis of the apparatus.

Embodiments of the present invention will now be described withreference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional side view of a first tool described in UKpatent application number 0116472.2 arranged in a first closedconfiguration;

FIG. 1 a is a plan view of the unwrapped profile of a control groovelocated relative to a control pin as shown in FIG. 1;

FIG. 2 is a cross-sectional side view of the first tool of FIG. 1arranged in a second closed configuration with downhole movement of asleeve restricted by the control groove and pin;

FIG. 3 is a cross-sectional side view of the first tool of FIG. 1arranged in an open configuration;

FIG. 3 a is a cross-sectional view taken along line 3-3 of FIG. 3;

FIG. 4 is a cross-sectional side view of the first tool of FIG. 1arranged in a third (emergency) closed configuration;

FIG. 5 is a cross-sectional side view of a second tool described in UKpatent application number 0116472.2 arranged in a first closedconfiguration;

FIG. 5 a is a plan views of the unwrapped profile of a control grooverelative to a control pin as shown in FIG. 5;

FIG. 6 is a cross-sectional side view of the second tool of FIG. 5arranged in a second closed configuration with downhole movement of asleeve restricted by the control groove and pin;

FIG. 7 is a cross-sectional side view of the second tool of FIG. 5arranged in an open configuration;

FIG. 7 a is a cross-sectional view taken along line 7-7 of FIG. 7 a;

FIG. 8 is a cross-sectional side view of the second tool of FIG. 5arranged in a third (emergency) closed configuration;

FIG. 9 is a cross-sectional side view of a third tool described in UKpatent application number 0116472.2 arranged in a first closedconfiguration with downhole movement of a sleeve restricted by a controlgroove and pin;

FIG. 9 a is a plan view of the unwrapped profile of a control groovelocated relative to a control pin as shown in FIG. 9;

FIG. 10 is a cross-sectional side view of the third tool of FIG. 9arranged in a second closed configuration with downhole movement of thesleeve restricted by the control groove and pin, and with the angularposition of the sleeve differing to that shown in FIG. 9;

FIG. 11 is a cross-sectional side view of the third tool of FIG. 9arranged in an open configuration;

FIG. 11 a is a cross-sectional view taken along line 11-11 of FIG. 11;

FIG. 12 is a cross-sectional side view of the third tool of FIG. 9arranged in an emergency closed configuration;

FIG. 13 is a cross-sectional side view of an embodiment of the presentinvention arranged in a first closed configuration with downholemovement of a sleeve restricted by a stop shoulder;

FIG. 14 is a cross-sectional side view of the embodiment shown in FIG.13 arranged in a second closed configuration with downhole movement ofthe sleeve restricted by a stop shoulder, and with the angular and axialposition of the sleeve differing to that shown in FIG. 13;

FIG. 15 is a cross-sectional side view of the embodiment of FIG. 13arranged in an open configuration;

FIG. 16 is a cross-sectional side view of the embodiment of FIG. 13arranged in an emergency closed configuration; and

FIG. 17 is a cross-sectional side view of a second embodiment of thepresent invention arranged in a first closed configuration.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The first tool shown in FIGS. 1 to 4 of the accompanying drawings is amulti-cycle circulating sub 2 defined by a plurality of internal partsmounted within a substantially cylindrical body 4. The body 4 is definedby three cylindrical members 6, 8, 10 threadedly connected to oneanother so as to define an elongate bore 12. The first body member 6 isthreadedly connected to an uphole end of the second body member 8 so asto provide a downwardly facing internal shoulder 14. The third bodymember 10 is threadedly connected to a downhole end of the second bodymember 8 so as to define an upwardly facing shoulder 16. An upper end 18of the first body member 6 is provided with an internal screw thread 20whilst a lower end 22 of the third body member 10 is provided with anexternal screw thread 24 so as to facilitate attachment of thecirculating sub 2 to adjacent components of a downhole string.

In addition to the cylindrical body members 6, 8, 10 as described above,the body 4 may be considered to also incorporate a cylindrical sleeve 26located in the elongate bore 12 between the downwardly and upwardlyfacing shoulders 14, 16. The sleeve 26 has an external diametersubstantially equal to the internal diameter of the second body member8. The external surface of the sleeve 26 is provided with two O-ringseals 28 for preventing axial fluid flow between said external surfaceand the internal surface of the second body member 8. The arrangement ofthe sleeve 26 within the second body member 8 is such that the sleeve 26may slide axially within the bore 12. However, as will be explainedhereinafter, such axial movement of the sleeve 26 occurs only duringemergency conditions. During normal use of the circulating sub 2, thecylindrical sleeve 26 is selectively retained in a predetermined axialposition relative to the second body member 8 by means of a shear pin30. One or more shear pins may be provided.

At the downhole end of the sleeve 26, three elements 32 integral withthe sleeve 26 extend inwardly from the interior surface of the sleeve 26(see FIG. 3 a) so as to provide three upwardly facing sleeve shoulders34. The elements 32 extend only a short distance into the bore 12 so asto maintain a circular fluid path 38 therepast. As will be understoodfrom the following discussion, the number of elements 32 may be variedso as to alter the number of cycles required to translate thecirculating sub between open and closed configurations. The elements 32are equi-spaced about the longitudinal axis of the circulating sub 2 anddefine slots 36 therebetween extending in a longitudinal direction. Thethree elements 32 are identical to one another and, accordingly, theslots 36 are identical to one another and equi-spaced about thelongitudinal axis of the circulating sub 2.

The body 4 is provided with six apertures 40 extending radially throughthe wall thereof so as to allow fluid communication between the bore 12and the exterior of the circulating sub. The apertures 40 lie in asingle plane orientated perpendicularly to the longitudinal axis of thebody 4. More specifically, the apertures 40 are provided in the secondbody member 8 and sleeve 26. The O-ring seals 28 are located uphole anddownhole of the apertures 40 so as to prevent an ingress into the bore12 of wellbore fluid located in the apertures 40.

The body 4 houses a plurality of internal parts including a piston 42and a helical compression spring 44 as principal components. The piston42 has a generally cylindrical shape with the upper part 46 thereofhaving a greater outer diameter than the lower part 48. The differencein diameter between the upper and lower parts 46, 48 of the piston 42provides a piston shoulder 50 (see FIG. 2 in particular). The externalsurface of the upper part 46 is circumscribed by a control groove 52having the unwrapped profile shown in FIG. 1 a. The control groove 52 isprovided in a direction having a first component parallel to theapparatus axis so as to allow axial movement of the piston 42, and asecond component extending circumferentially so as to allow rotation ofthe piston 42. The control groove 52 is thereby formed to produce rotaryindexing of the piston 42 as the piston 42 moves axially.

An O-ring seal 54 and wear ring 56 are provided on the external surfaceof the piston 42 above the groove 52. The piston 42 is also providedwith a bore 58 having a sufficiently large diameter to allow the passageof wireline or coil tubing tools. It will be understood from FIGS. 1 to4 that the external diameter of the piston upper part 46 issubstantially equal to the internal diameter of the second body member8, that the external diameter of the piston lower part 48 issubstantially equal to the internal diameter of the sleeve 26, and thatthe diameter of the piston bore 58 is substantially equal to thediameter of the circular fluid path 38 past the three sleeve elements32. The dimensions of the piston 42 relative to the body 4 are such asto allow ready axial movement of the piston 42 within the body 4.

The piston 42 is located in the bore 12 of the second body member 8 withthe piston shoulder 50 positioned uphole of a spring shoulder 60 definedby the uphole end of the sleeve 26. The compression spring 44 extendsbetween the spring shoulder 60 and the piston shoulder 50 so as to biasthe piston 42 in an uphole axial direction towards the first body member6. A bearing 62 is located between the spring 44 and the piston shoulder50 so as to allow the piston 42 to rotate relative to the spring 44 morereadily. Uphole displacement of the piston 42 is limited by thedownwardly facing shoulder 14. The body 4 and the piston 42 thereby forma piston spring chamber 64 which is sealed by means of the piston O-ringseal 54 or glyd ring and a further O-ring seal 66 or glyd ring mountedin the inner surface of an uphole portion of the sleeve 26. The furtherseal 66 may be provided on the piston 42. The axial movement of thepiston 42 within the bore 12 is assisted by the provision of vent holes68 which, when in use, vent the piston spring chamber 64 to the pistonbore 58. Four vent holes 68 are provided. The diameter of each vent hole68 determines the degree of damping provided to the piston 42.Increasing the diameter of a vent hole 68 decreases the damping. Therate of piston movement may be thereby controlled and axial drillingvibration and shock inputs counteracted.

As shown in FIG. 1, the length of the piston 42 is slightly less thanthe distance between the downwardly facing shoulder 14 and the threeupwardly facing sleeve shoulders 34. Nevertheless, the piston 42 hassufficient length to extend downwardly past the apertures 40 of the body4 when located in abutment with the downwardly facing shoulder 14. TwoO-ring seals 70 or glyd rings located uphole and downhole of the bodyapertures 40 in the inner surface of the sleeve 26 prevent undesirableingress of fluid in said apertures 40 into the circulating sub 2 betweenthe sleeve 26 and piston 42 (i.e. prevents fluid leakage past the pistonin the closed position). Nevertheless, the piston 42 is provided withsix flow ports 72 which may be aligned with the apertures 40 throughaxial displacement of the piston 42 so as to permit a flow of wellborefluid between the annulus and the interior of the circulating sub 2.More specifically, the flow ports 72 i.e. in a single plane orientatedperpendicularly to the longitudinal axis of the piston 42. The flowports 72 extend radially through the walls of the piston 42 and are of asimilar diameter to the apertures 40. The arrangement of the flow ports72 relative to the apertures 40 is such that, when the piston 42 islocated in a closed position as shown in FIGS. 1 and 2, the flow ports72 locate uphole of the apertures 40 and neighbouring seals 70 so as toisolate the bore 12 from the annulus, whereas when the piston 42 islocated in an open position as shown in FIG. 3, the flow ports 72 alienwith the apertures 40 and thereby provide a fluid pathway between theannulus and the bore 12.

The downhole end of the piston 42 is provided with three axiallyextending slots 74 (only two of which are visible in the accompanyingdrawings). The piston slots 72 extend through the full thickness of thepiston wall and effectively provide three elements 76 downwardlyprojecting from the downhole end of the piston 42. The three pistonelements 76 are equi-spaced about the longitudinal axis of thecirculating sub 2 and have a length and circumferential widthsubstantially identical to that of the sleeve slots 36. The relativesizes of the sleeve slots 36 and piston elements 76 are such that thepiston elements 76 may align with and slide axially into the sleeveslots 36. Clearly, the circumferential width of the sleeve elements 32relative to the piston slot 74 are also such that, when aligned, thepiston slots 74 may slide axially over the sleeve elements 32. As withthe piston elements 76 and sleeve slots 36, the circumferential widthsof the piston slots 74 and sleeve elements 32 are substantially equal.The purpose of this equality of circumferential widths is to ensurethat, when the elements 32, 76 are respectively engaged with the slots34, 36, the relative rotation possible between the piston 42 and 44 isminimal. As will be understood from the following discussion, thepurpose of the element/slot engagement is more specifically to preventrotation of the piston 42 relative to the body 4 in one particulardirection during movement of the piston 42 towards the open positionshown in FIG. 3. Thus, an attempt by the piston 42 to rotate relative tothe body 4 whilst the elements 32, 76 and slots 36, 74 are engaged willresult in abutment of each sleeve element 32 with an adjacent pistonelement 76 at longitudinally extending edges thereof. Thus, in order tominimise possible relative rotation between the piston 42 and body 4, itis important for the aforementioned abutting edges to be in abutmentwith one another or at least very close to one another as the piston 42begins movement towards the open position. The relative angularpositions of the remaining longitudinally extending edges of the sleeveand piston elements 32, 76 which do not tend to abut one another in use(due to the direction of relative piston/body rotation) are notcritical. To this extent, equality of the element and slotcircumferential width is not essential to the operation of thecirculating sub 2.

As most clearly shown in the expanded view of FIG. 1, a removableannular nozzle 78 is mounted in the piston bore 58 at an uphole end ofthe piston 42. The nozzle 78 is secured against an upwardly facingshoulder 80 defined in the piston bore 58 with an annular retaining ring82. The retaining ring 82 is itself located in an annular grooveprovided in the piston bore 58. Fluid flow between the nozzle 78 andpiston 42 is prevented by means of an O-ring seal 84. The purpose of thenozzle 78 is to provide a pressure drop in fluid flow passing throughthe piston bore 58. The nozzle 78 may be selected so as to provide adesired restriction in the piston bore 58 and thereby initiate downholeaxial movement of the piston 42 within the body 4 at a given flow rateof fluid through the circulating sub 2.

A control pin 86 extends through the wall of the second body 8 so as toproject into the bore 12 and locate in the control groove 52. Thecontrol pin 86 is secured in position by means of a retaining plug 88.One or more control pins may be provided. The shear pin 30 connectingthe second body member 8 and sleeve member 26 also extends through anaperture through the wall of body member 8 and is retained in positionby means of a retaining plug.

When in use, the multi-circulating sub 2 forms part of a downhole stringthrough which well bore fluid may be pumped in order to operateequipment such as an anchor packer or a drilling tool, for example, aturbo drill or a positive displacement motor. FIGS. 1 and 1 a show thecirculating sub 2 arranged with the piston 42 located in an inactivatedclosed position. In this inactivated position, the piston 42 is locatedin abutment with the downwardly facing shoulder 14 of the second bodymember 8. The downhole end of the piston 42 (including the plurality ofpiston elements 32) is located uphole of the plurality of upwardlyfacing sleeve shoulders 34. Furthermore, the control pin 86 is locatedat one of six inactivated groove positions X within the control groove52. The piston 42 will remain in the inactivated position until apredetermined flow of wellbore fluid through the circulating sub 2 isgenerated. As already indicated, the predetermined fluid flow may beadjusted by changing the dimensions of the nozzle 78. Once thepredetermined fluid flow is generated or exceeded, the piston 42 willattempt to move to the activated open position shown in FIG. 3.

However, the axial movement of the piston 42 is controlled by theinteraction of the control pin 86 and the control groove 52, and thepiston 42 will be prevented from moving to the activated position unlessthe control pin 86 is located at one of three inactivated groovepositions XX within the control groove 52 (see FIG. 1 a) immediatelybefore the predetermined flow rate is produced. If the control pin 86 isnot located at one of said three inactivated groove positions A, thenthe axial movement of the piston 42 will result in the control pin 86moving to one of three intermediate groove positions Y (see FIG. 1 a).Although displaced axially, no part of the piston 42 has moveddownwardly past the upwardly facing sleeve shoulders 34 when the controlpin 86 is located at any one of the intermediate groove position Y see(FIG. 2). With the control pin 86 located in an intermediate grooveposition Y, the downhole ends of the piston elements 76 are abutting thesleeve shoulders 34. The relative angular position of the piston 42 andsleeve 26 is such that the piston and sleeve elements 76, 32 do notalign with the sleeve and piston slots 36, 74. With the piston 42located in either of the inactivated or intermediate positions shown inFIGS. 1 and 2 respectively, the flow ports 72 remain uphole of the bodyapertures 40 and sealed therefrom by means of the adjacent O-ring seal70. Thus, a discharge of wellbore fluid from the sub 2 through theapertures 40 is prevented.

When the control pin 86 is located in one of the aforementioned threeinactivated positions XX within the control groove 52 immediately beforethe predetermined flow rate is generated or exceeded, the profile of thecontrol groove 52 allows the piston elements 76 to move rotationallyinto alignment with the sleeve slots 36 and to then allow the piston 42to move axially downhole without further rotation (see FIGS. 3 and 3 a).As the piston 42 moves downhole relative to the body 4, the control pin86 moves within the control groove 52 from position XX to one of threeactivated groove positions Z (see FIG. 1 a). With the control pin 86located in one of the three activated groove positions Z, the flow ports72 in the piston 42 align with the body apertures 40 so as to allow thedischarge of wellbore fluid from the string into the surroundingwellbore annulus.

Also, with the circulating sub 2 arranged in the open configuration, theclosed ends of the piston slots 74 abut the upwardly facing sleeveshoulders 34.

Movement of the piston 42 is assisted by the four vent holes 68 whichallow fluid to flow between the piston spring chamber 64 and the pistonbore 58 as the piston 42 moves axially and varies the volume of thespring chamber 64.

It will be understood that the piston and sleeve elements 76, 32 must bearranged so as to align with the sleeve and piston slots 36, 74 when thecontrol pin 86 moves from the aforementioned inactivated positions XX tothe activated groove positions Z. More importantly, the piston andsleeve elements 76, 32 should be arranged relative to one another sothat should the piston 42 attempt to rotate (perhaps under the action offluid imbalance in the piston bore) in opposition to the control grooveand pin, adjacent piston and sleeve elements 76, 32 abut one another andprevent piston rotation. In this way, the application of undesirableforces on the control pin 86 is prevented. The risk of the control pin86 becoming sheared and/or the piston 42 becoming jammed is thusreduced.

In order to move the control pin 86 from an intermediate groove positionY or activated groove position Z and move the piston 32 towards theinactivated position shown in FIG. 1, the rate of wellbore fluid flowthrough the circulating sub 2 is reduced below the predetermined rate soas to allow the compression spring 44 to relax and press the piston 42into abutment with the first body member 6. Movement of the circulatingsub 2 from an open configuration to a closed configuration may bethereby readily achieved. However, circumstances may arise where thepiston 42 becomes jammed in a downhole position (perhaps due to debris)to the extent that the uphole biasing force of the compression spring 44is insufficient to release the piston 42 even when the flow rate isreduced to zero. A situation may therefore arise where closing of thecirculating sub 2 becomes problematic.

In the event that the circulating sub 2 becomes jammed in an openconfiguration, an attempt to move the circulating sub 2 to a closedconfiguration can be made by increasing the flow of fluid through thecirculating sub 2 so as to shear the shear pin 30 and move the piston42, together with the sleeve 26, downhole towards the third body member10. It is envisaged that a greater resultant force on the piston 42 canbe generated by a flow of fluid downhole through the borehole 12 than bythe compression spring 44. Thus, it may well be possible to move ajammed piston 42 downhole by means of dynamic fluid pressure incircumstances where the compression spring 44 is unable to move thejammed piston 42 uphole. However, since downhole movement of the piston42 is limited in the open configuration by means of the sleeve elements32 (so as to ensure alignment of the body apertures 40 and the flow port72), further downhole movement of the piston 42 must be accompanied by adownhole movement of the sleeve 26. The force applied by the fluid flowto the piston 42 must therefore be sufficient not only to release thepiston 42, but also to shear the shear pin 30 and thereby allow movementof the sleeve 26. Once a sufficient force is generated to release thepiston 42 and shear the shear pin 30, the piston 42 and sleeve 26 movedownhole to an emergency closed position. The profile of the controlgroove 52 is such as to allow the further downhole movement of thepiston 42. As shown in FIG. 4, the further downhole movement of thepiston 42 is limited by abutment of the sleeve 26 with the upwardlyfacing shoulder 16 defined by the third body member 10. In the emergencyclosed configuration, the portions 90 of the body apertures 40 definedby the sleeve 26 remain aligned with the flow port 72 but locatedownhole of the portions 22 of the body apertures 40 defined by thesecond body member 8. Also, in the emergency closed configuration, thecontrol pin 86 locates in one of three extended groove positions ZZ.

Variations and modifications to the above described tool will beapparent to the reader skilled in the art. For example, the controlgroove 52 may have an alternative profile with a different number ofinactivated, intermediate, activated and extended groove positions. Thecontrol groove 52 shown in FIG. 1 a has a profile which causes thepiston 42 to rotate through 120° when moving axially between successiveintermediate or activated groove positions Y, Z. The profile may bealtered so that the piston 42 rotates through a different angle whenmoving between these positions (consequential alternation to thearrangement of piston and sleeve elements 76, 32 may also be required aswill be apparent to the skilled reader).

The circulating sub 2 shown in FIGS. 1 to 4 may be regarded as atwo-cycle circulating sub in that two cycles of pressurising the sub inorder to move the piston 42 axially downhole must be undertaken beforethe sub 2 will be translated from a closed configuration into an openconfiguration. The number of cycles is determined not only by theprofile of the control groove 52, but also by the arrangement of thepiston and sleeve element 76, 32. It will be understood that the numberof cycles will be changed by altering the arrangement of the piston andsleeve elements 76, 32 without necessarily altering the profile of thecontrol groove 52. This is because, although the activated groovepositions Z of the control groove 52 may allow downhole movement of thepiston 42 into an open position, piston movement to the open positionwill not be realised unless the piston and sleeve elements 76, 32 alignwith the sleeve and piston slots 36, 74. Thus, a six-cycle circulatingsub 102 is shown in FIGS. 5 to 8 of the accompanying drawings, whereinthe profile of the control groove is identical to that of the firsttool. Indeed, the six-cycle circulating sub 102 differs from thetwo-cycle circulating sub 2 only in the arrangement of the piston andsleeve elements.

As can be seen most clearly from FIG. 7 a, the sleeve 126 and piston 142of the second tool 102 each comprise merely a single element 132, 176having a semicircular shape. The piston element 176 is arranged relativeto the control groove 52 and the sleeve element 132 so that the controlpin 86 is able to move to only one of the activated groove positions Z.Movement to the remaining two activated groove positions Z is preventedby abutment of the downhole end of the piston element 176 with theupwardly facing sleeve shoulder 134 defined by the sleeve element 132.However, when the sleeve and piston elements 134, 176 are positionedrelative to one another so as to allow movement of the control pin to anactivated groove position Z, abutment of the longitudinally extendingedges 133, 177 of the sleeve elements 132 and piston elements 176ensures rotation of the piston 142 relative to the second body member 8in opposition to the control groove and pin is resisted. It will beunderstood therefore that the control groove 52 and sleeve/pistonelements 132, 176 combine to provide a six-cycle indexing mechanism.

In order to provide improved versatility, the elements provided on thesleeve and piston may be respectively detachable from the sleeve andpiston. This may be achieved by defining the elements on a cylindricalportion which is screw threadedly engageable with the lower part of thesleeve or piston. In this way, the cycle characteristics of acirculating sub may be rapidly and conveniently altered.

As shown in FIG. 8, the six-cycle circulating sub 102 may be moved to anemergency closed configuration (as with the first tool 2) by increasingthe flow rate through the circulating sub 102 and shearing the shear pin30.

A third tool 202 is shown in FIGS. 9 to 12 of the accompanying drawings.The third tool 202 is a six-cycle circulating sub differing from thesecond tool 102 only in the arrangement of the downhole portions of thesecond body member 208, sleeve 226 and piston 242. The arrangement ofthese components is such that, when the piston is in a closed positionas shown in FIGS. 9 and 10 (or an emergency closed position as shown inFIG. 12), wellbore fluid may flow through the interior of thecirculating sub 202 as in the case of the first and second tools;however when the piston 242 is in an open position as shown in FIG. 11,the bore 12 through the circulating sub 202 is closed and all wellborefluid flowing downhole through the circulating sub 202 is directed intothe annulus by the body apertures 40.

More specifically, the downhole portions of the sleeve 226 and piston242 are arranged with an asymmetric configuration. The piston 242defines a piston bore 258 having an upper portion coaxially arrangedwith the longitudinal axis of the circulating sub 202 and a lowerportion located downhole of the flow ports 72 which extends downhole atan angle relative to the longitudinal axis of the circulating sub 202.Accordingly, the downhole end of the piston bore 258 opens at a locationoffset from the longitudinal axis of the apparatus 202. This offsetlocation provides a downhole facing piston shoulder 259 extendinginwardly into the bore 12 of the circulating sub 202. A single pistonelement 276 extends downwardly from the shoulder 259. The downhole endof the sleeve 226 has a reduced diameter defining a restricted bore 227within an axis offset relative to the longitudinal axis of thecirculating sub 202. Uphole of the reduced diameter, the sleeve 226 isprovided with four ports 229 which extend radially through the thicknessof the sleeve 226.

When in the closed configuration as shown in FIGS. 9 and 10, wellborefluid may flow through the circulating sub 202 via the piston bore 258,about the downwardly facing piston shoulder 259 and through therestricted sleeve bore 227. In FIG. 9, the circulating sub 202 is shownwith the piston 242 displaced downhole against the bias of thecompression spring 44 by means of an appropriate flow rate of well borefluid. Displacement of the piston 242 into an open position is preventedby abutment of the piston element 276 against a single sleeve element232 defining the restricted bore 227. The circulating sub 202 is shownin FIG. 10 cycled to a further closed configuration with the piston 242having been rotated within the second body member 208. Again, movementof the piston 242 into the open position is prevented by abutment of thepiston element 276 against the sleeve element 232. However, with thecirculating sub 202 cycled to the configuration shown in FIGS. 11 and 11a, it will be seen that the piston 242 has rotated sufficiently for thepiston element 276 to alien with the restricted bore 227 (acting as asleeve slot) allowing the piston 242 to move further downhole relativeto the sleeve 226. In so doing, the piston flow ports 72 align with thebody apertures 40 (allowing flow to the annulus) and the downwardlyfacing piston shoulder 259 closes the restricted sleeve bore 227(preventing fluid flow within the bore 12 downhole past the second bodymember 208). Fluid flow through the four ports 229 is not possible inthe open and closed piston positions of FIGS. 9, 10, 11 and 11 a due tothe sealing of these ports by means of the second body member 208.

As described with relation to the first and second tools, the third tool202 may be moved to an emergency closed position in the event that thepiston 242 becomes jammed and the biasing force of the compressionspring 44 is insufficient to return the piston 242 to its originaluphole position in abutment with the first body member 6. Again, asdescribed in relation to the first and second tools, the emergencyclosed configuration is achieved by increasing the flow of fluid throughthe bore 12. The flow rate is increased until the downhole force appliedto the piston 242 is sufficient to release the piston 242 and shear theshear pin 30. The piston 242 and sleeve 226 are then moved downhole.Downhole movement of the piston 242 and sleeve 226 is limited byabutment of the sleeve 226 with the third body member 10. Although therestricted sleeve bore 227 remains sealed by the downwardly facingpiston shoulder 259, flow through the bore 12 into the third body member10 is permitted by means of the ports 229 provided in the sleeve 226.Flow through the ports 229 is possible with the sleeve 226 abutting thethird body member 10 by virtue of a circumferential recess 231 providedin the interior surface of the second body member 208 at a downholeportion thereof. More specifically, the recess 231 is located uphole ofthe third body member 10 and downhole of the four ports 229 when thesleeve 226 is located in a non-emergency position (i.e. when retained bythe shear pin 30 as shown in FIGS. 9 to 11 a). The circumferentialrecess 231 has sufficient downhole length for wellbore fluid to flowthrough the sleeve ports 229, around and beneath the sleeve element 232,and into the third body member 10.

It will be understood that any of the above described tools may be movedto the emergency closed configuration by running means for closing thepiston bore. For example, a ball or dart may be dropped or run on a wireline downhole through the apparatus so as to locate in the piston 42,142, 242 and block the piston bore. The shear pin 30 will then shear andthe apparatus will close. The ball or dart may then be recovered andcirculation through the apparatus restored. Alternatively, a burst discin the dart may be ruptured so as to allow circulation.

It has been found by the applicant that, although the tools describedabove in relation to FIGS. 1 to 12 have beneficial operatingcharacteristics, the performance of the tools can nevertheless beimproved with certain modifications. These modifications are describedbelow in relation to first and second embodiments of the presentinvention shown in FIG. 1316 and FIG. 17 respectively of theaccompanying drawings. The first embodiment is an improved six-cyclecirculating sub 302. Apart from the modifications described below, theimproved circulating sub 302 is identical to the third circulating sub202 of FIGS. 9 to 12 and, accordingly, like reference numerals have beenused to identify like components in the accompanying drawings.

A first modification comprised in the embodiment of FIGS. 13 to 16 isthe provision of a second set of vent holes 369 to compliment theoriginal set of vent holes 368 provided in the piston 242. The two setsof vent holes 368,369 provide for the venting of fluid from the pistonspring chamber. Axial movement of the piston 242 is thereby assisted.However, whereas the original set of vent holes 368 are provided in thepiston 242 for venting of fluid from the piston spring chamber into thepiston bore 258, the second set of vent holes 369 are provided in thesecond body member 208 and thereby allow venting of fluid from thepiston spring chamber to the exterior of the tool 302 (i.e. in use, to awellbore annulus). Each set of vent holes 368, 369 comprises four holes(although, for either set, an alternative number of holes may beprovided).

One of the two sets of vent holes 368,369 should be occluded dependingon particular operational requirements. In the arrangement shown inFIGS. 13 to 16, each hole 369 of the second set of vent holes isoccluded with a NPT plug. Venting is therefore achieved via the originalset of vent holes 368. However, the original set of vent holes 368 mayalternatively be occluded with NPT plugs with the second set of ventholes 369 being used to vent the piston spring chamber (as shown inFIGS. 14 to 16). With the second set of vent holes 369 open, the pistonspring chamber becomes filled, in use, with wellbore fluid. The piston242 is thereby exposed to wellbore fluid static pressure. This externalfluid pressure will be less than the fluid pressure within the pistonbore 258 when fluid is being pumped from the surface through theapparatus. With the annulus fluid pressure less than that in the pistonbore 258, the resultant axial force will act in a downhole direction andhave a greater magnitude than if the spring chamber was vented to thepiston. This can have the benefit of reducing a tendency for the piston242 to undesirably cycle due to vibration. In other words, the pressuredifferential across the length of the piston will hold the piston in ahalf-down position so the apparatus remains in a closed configurationwhilst a drilling operation is completed.

When the improved sub 302 is arranged so that the spring chamber isvented to the wellbore annulus, the flow rate required to move thepiston will be lower than when the spring chamber is vented to thepiston bore 258. Also, when venting to the wellbore annulus, theimproved sub 302 may be provided with a larger piston bore (or a pistonnozzle having a larger bore). This can be advantageous since pressurelosses across the sub 302 may be thereby reduced to allow increasedpressure and greater system flow rates to be applied during drillingoperations.

A high degree of axial vibration can occur when drilling hard rockformations and it is critical to drilling performance that the piston242 is prevented from bouncing to such an extent that the body apertures40 are opened. In venting the spring chamber to the annulus, the flowrate used during drilling will be considerably higher than the flow raterequired to move the piston. In other words, during a drillingoperation, the flow rate through the piston bore 258 will be sufficientto force the piston 242 downhole and retain the piston 242 in a closedposition against uphole forces generated by axial vibration. Incontrast, when the spring chamber is vented to the piston bore 258, theadditional flow rate, used during drilling, over that used to move thepiston 242, is reduced to an extent whereby there may be insufficientdownhole force applied to the piston 242 to resist an uphole bouncing ofthe piston 242. Regardless of whether the spring chamber is vented tothe annulus or the piston bore, an undesirable bouncing of the piston242 can be limited by reducing the cross-sectional area of the flowpassage from the spring chamber. In this way, the ease with which fluidmay flow into the spring chamber so as to allow an uphole movement ofthe piston 242 is limited. Piston movement is thereby provided with adegree of dampening. The cross-sectional area of the vent passage may bereduced by occluding one or more vent holes with a plug or partiallyoccluding one or more vent holes with a plug having one or moreapertures provided therein.

With particular regard to the expanded partial views shown in FIGS. 14to 16, it will be seen that the improved sub 302 comprises modificationsto the arrangement of O-ring seals located between the second bodymember 208, the sleeve 226, and the piston 242. The improved sub 302includes an additional O-ring seal 380 between the piston 242 and thesleeve 226, and a further additional O-ring seal 382 between the sleeve226 and the second body member 208. The first additional O-ring seal 380ensures that fluid within the piston bore 258 does not leak to thewellbore annulus via the flow ports 72 and second set of vent holes 369.The second additional O-ring seal 382 ensures that wellbore fluid cannotflow between the second body member 208 and the sleeve 226 via the bodyapertures 40. This is of particular importance when the second set ofvent holes 369 are occluded so as to prevent ingress of wellbore fluidinto the piston spring chamber. Without the second additional O-ringseals 382, wellbore fluid would flow into the piston spring chamber whenthe sub 302 is arranged in the emergency closed position.

A third additional O-ring seal 384 is provided between the sleeve 226and the second body member 208 so that, when in the emergency closedposition, wellbore fluid is prevented from accessing the flow ports 72in the piston 242 via the body apertures 40. A fourth additional O-ringseal 386 is located between the sleeve 226 and the second body member208 so as to assist in ensuring that fluid flows between the piston bore258 and the wellbore annulus via the flow ports 72 and body apertures 40without undesirable leakage between the sleeve 226 and the second bodymember 208. Also, a PTFE bearing support ring 388 is mounted on thesleeve 226 so as to assist in relative rotation between the sleeve 226and the piston 242. A yet further modification is the provision of alocation rim (i.e. an annular recess) on the uphole end of the sleeve226 for receiving the downhole end of the spring. The spring locationrim is not apparent in the enclosed drawings. It will be understood thatany of the aforementioned O-ring seals may be replaced with or types ofstatic seal.

Although the improvements shown in FIGS. 13 to 16 have been described asmodifications to the third tool shown in FIGS. 9 to 12, the describedmodifications may also be advantageously applied to the tools shown inFIGS. 1 to 8. Indeed, the second embodiment of the present inventionshown in FIG. 17 is a modification of the tool shown in FIGS. 5 to 8 ofthe accompanying drawings. Apart from the modifications described below,the improved circulating sub 402 of FIG. 17 is substantially identicalto the circulating sub 102 of FIGS. 5 to 8 and, accordingly, licereference numerals have been used to identify like components in theaccompanying drawings.

As with the first embodiment 302, the second embodiment 402 comprisestwo sets of vent holes 468,469 for venting the piston spring chamber.The set of vent holes 469 provided in the body comprises a single venthole. Each hole of the second set of vent holes 468 is occluded with aNPT plug. Also, the body of the sub 402 is provided with a set ofapertures 440 for allowing fluid communication between the bore of thesub and the exterior thereof. Each aperture 440 is provided as a fluidpassageway arranged to direct fluid (flowing therethrough from the subbore) in an uphole direction. To this end, each fluid passageway 440 hasa longitudinal axis orientated at an acute angle to and in the sameplane as the longitudinal axis of the sub 402. Each passageway 440 isalso provided with a nozzle 441. The plurality of flow ports 472provided in the piston 142 communicate with the single body aperture 440by means of an annular fluid communication groove 443. The annulargroove 443 is provided in the interior surface of the body. The upholeorientation of the body aperture 440 results in an uphole flow ofannulus fluid being boosted by fluid exiting the body aperture 440 withan uphole flow component.

A further modification provided to the sub 402 is the provision of threesets of stabiliser blades 445 immediately downhole of the body aperture440. Furthermore, the sleeve 426 may be provided in two components so asto ease manufacture. The two components of the sleeve 426 may be pinnedor screw threadedly engaged with one another. The first embodiment shownin FIGS. 13 to 16 may also be provided with a multi-piece sleeve toassist with manufacture.

Furthermore, as already mentioned in relation to the tools of FIGS. 1 to12, a dart may be run so as to block the piston bore and allow asufficient build up of pressure to move a tool into the emergency closedconfiguration. The first embodiment of the present invention is shown inFIG. 16 located in the emergency closed configuration with a dart 390blocking the piston bore 258. The dart 390 is shown in greater detail inFIG. 13 wherein it can be seen that the dart comprises a through bore392 occluded at an uphole end thereof by a burst disc 394. The use ofsuch a dart 390 allows fluid to be pumped through the sub 302 once thesub 302 has been moved to the emergency closed position. This isachieved by increasing the fluid pressure within the sub 302 so as torupture the burst disc 394 and thereby allow access to the dart throughbore 392. The pressure required to rupture the burst disc 394 will begreater than that required to shear the pin 30.

The present invention is not limited to the specific embodimentsdescribed above. Variations and modifications will be apparent to thereader skilled in the art.

1. Apparatus for selectively providing fluid communication between theinterior of a downhole assembly and the exterior thereof, said apparatuscomprising: a body incorporating a wall provided with at least oneaperture extending therethrough; a piston having a longitudinal boreextending therethrough and being slidably mounted in the body so as tobe movable between a first position relative to the body preventingfluid communication between the bore of the piston and the exterior ofthe body via the or each aperture and a second position relative to thebody permitting fluid communication between the bore of the piston andthe exterior of the body via the or each aperture; and controlling meansfor controlling the movement of the piston between the first and secondpositions, the controlling means comprising: a control member slidablein the body and movable by fluid pressure in the body in a first axialdirection relative to the body; a spring biasing the control member inan opposite axial direction of the body; a pin secured to one of thebody and the control member; and a control groove in which a portion ofthe pin is received formed in the other of the body and the controlmember, the control groove being shaped to limit axial displacement ofthe control member generated by pressure variations in the body suchthat only after a predetermined number of movements of the controlmember to a first axial position is the control member able to move to asecond axial position so as to displace the piston from one of the firstand second piston positions to the other of the first and second pistonpositions; wherein the controlling means further comprises a firstelement connected to the control member so as to prevent relativerotation between the first element and the control member, and a secondelement connected to the body so as to prevent relative rotation betweenthe second element and the body, wherein the arrangement of saidelements is such that, in the first axial position of the controlmember, the first and second elements normally abut one another so as toresist axial movement of the control member toward the second axialposition, said elements locating offset relative to one another so as toallow movement of the control member to the second axial position onlyafter a predetermined number of movements of the control member to thefirst axial position; wherein the spring is located in a chamber definedbetween the control member and the body; and at least one vent openingis provided in the body for venting fluid located in the chamber to theexterior of the body, and wherein the arrangement of said elements issuch that, as the control member moves from said first axial position tosaid second axial position, increasing lengths of said elements locateadjacent one another so as to prevent relative rotation, in at least onedirection, of the control member and body, said relative rotation beingrelative rotation which presses the control pin against the controlgroove.
 2. Apparatus as claimed in claim 1, wherein at least one ventopening is provided in the control member for venting fluid located inthe chamber to the exterior of the body.
 3. Apparatus as claimed inclaim 2, wherein the or each vent opening in the control member isoccluded so as to prevent a passage of fluid therethrough.
 4. Apparatusas claimed in claim 1, wherein said first element remains axially spacedfrom said second element until the control member is axially moved tothe first axial position.
 5. Apparatus as claimed in claim 1, whereinthe arrangement of the first and second elements is such that, when saidelements are offset, the control pin is received in one of a pluralityof portions of control groove allowing the control member to move to thesecond axial position.
 6. Apparatus as claimed in claim 1, wherein thearrangement of the first and second elements is such that, when saidelements are offset, the control pin is received in a portion of thecontrol groove, allowing the control member either to displace thepiston in said first axial direction from the first piston position tothe second piston position and then to a third piston positionpreventing fluid communication between the bore of the piston and theexterior of the body via the or each aperture, or to displace the pistonin said first axial direction from the second piston position to thefirst piston position and then to a third piston position permittingfluid communication between the bore of the piston and the exterior ofthe body via the or each aperture.
 7. Apparatus as claimed in claim 6,wherein the control groove comprises a plurality of said portionsallowing displacement of the piston to said third piston position. 8.Apparatus as claimed in claim 1, wherein movement of the control memberin said first axial direction past the second axial position isprevented by means of an abutment of the second element with the controlmember or a component connected thereto.
 9. Apparatus as claimed inclaim 8, wherein the second element is releasably connected to the body.10. Apparatus as claimed in claim 9, wherein the second element isreleasably connected to the body by means of a shear pin.
 11. Apparatusas claimed in claim 1, wherein, when in the second piston position, thepiston is located so as to seal a fluid pathway through the apparatusand thereby, in use, direct fluid flowing into said apparatus throughthe or each aperture.
 12. Apparatus as claimed in claim 1, wherein theor each aperture extending through the body wall is arranged so thatwellbore fluid flowing in use through the or each aperture from theinterior of the apparatus is directed in a direction having a componentparallel to the longitudinal axis of the apparatus.